This application relates to wheelchair lifts having a stowable platform and a dual function safely barrier pivotably secured to the inboard end thereof, which barrier is actuated by a link to variously raise the barrier to a safety position and lower it to a bridging position in synchrony with the position of the platform. More particularly the invention relates to dual parallelogram type lifts employing an articulated lever assembly having a sliding block for leveraging the platform from a horizontal transfer orientation to a vertical, or over-vertical stowage position, in which a spring assist system comprising a gas spring acting on one member of the articulated lever assembly and a lever arm linking a second arm of the articulated lever assembly to the barrier co-operate to actuate the barrier from a raised position when the platform is away from the transfer level to a lowered position to act as a bridge plate at the transfer level. Also disclosed is an anti-free fall assembly comprising a pin on the slide block which engages one of the articulated arms to lock it during the initial stage of deploy from a vertical stowage position.
Parallelogram type wheelchair lifts are offered by a number of manufacturers, including The Braun Corporation of Winamac, Ind. in its L900 series of lifts, as shown in its U.S. Pat. No. 5,261,779, and by Ricon Corporation of Pacoima, Calif. in its S-series of lifts, as shown in U.S. Pat. No. 4,534,450 and expired U.S. Pat. No. Re 31,178. These lifts employ various mechanisms to cause the platform to move arcuately upward from the horizontal transfer level to a vertical or over-vertical stowage position. One system involves the use of an articulated lever assembly comprising a pair of arms of unequal length pivotably connected to each other at one end, and pivotably connected at their other ends respectively to: a) the vertical lift arm end link, at the bottom end of which is pivotally secured the platform, and b) the inboard end of the platform. As the hydraulic ram in the lifting assembly is actuated, lifting the platform from the ground level toward the transfer level, a sliding block, pivotally secured at the common center of the two arms, comes into contact with the lower arm of the parallelogram. As the lifting continues and the end link approaches the lower arm, the lower longer arm of the lever assembly is pushed downwardly. In turn this causes the outboard end of platform to rotate upwardly to the stowed position.
To prevent platform free fall, a number of strategies are employed as set forth in U.S. Pat. No. 5,806,632 issued Sep. 15, 1998, the disclosure of which is hereby incorporated by reference. These strategies include stud and slot arrangements of the Braun Model L211 U, Ricon""s Saucier U.S. Pat. No. 5,605,431 (FIGS. 13-15) and a diagonal spring arrangement across the arms of the articulated lever arm assembly as set forth in the aforesaid U.S. Pat. No. 5,806,632.
The outboard end of the platform typically includes a roll stop safety barrier. A variety of actuation strategies are employed, including cables, chains and levers, with or without gas spring or linear actuator assist. Likewise the inboard end of lift platforms are provided with a variety of strategies for actuating inboard barriers. An example is a cam actuated cable system of Saucier, et al., U.S. Pat. No. 5,605,431 (1997) which was commercially available at least as early as Mar. 16, 1992 as the Ricon Model S 5003. This system employs a bell crank and cable. In that system, the lifting parallelogram actuates a cable, the length of which is controlled by a cam assembly pivoted to the lifting end link or an arm of the parallelogram so that as the platform moves, an interior barrier is raised or lowered by the other end of the cable. The articulated lever arm anti-free-fall assembly is not involved in the inboard barrier actuation.
Cable systems however have a number of serious drawbacks, among them being that the cable is difficult to adjust precisely, thereby requiring frequent readjustments, as it stretches in use and tends to lengthen or shorten with temperature. In addition, a cable can fray or break in use, and has limited strength. The barrier position varies under all these conditions and can become out of synchrony with the platform position. In some cases the barrier could prematurely descend to a near-horizontal position prior to the platform reaching the transfer level, in which case it could impact the side of the vehicle or the sill lip at the entry causing damage to the lift and/or vehicle.
Accordingly, there is a need for an improved positive inboard barrier actuation system that does not have the drawbacks of such cable systems.
This invention includes the following features, functions, objects and advantages in an improved inboard barrier assembly: An inboard safety barrier/bridgeplate which is directly actuated by the articulated lever arm system of the lift; A safety barrier which does not make use of cables; An inboard safety barrier which is precisely and consistently coordinated with the position of the lift; an inboard safety barrier which has the dual function of use as a bridgeplate in a lowered, generally horizontal position. Other objects and advantages will be evident from the description, drawings and claims.
The dual function, inboard barrier/bridgeplate assembly of the invention comprises a generally rectangular plate pivotally mounted to the platform assembly, preferably by pivots mounted coaxially with the lower push arm pivots, which are located on each side of the inboard edge of the platform. The plate is mounted to the pivots by a side brackets of selected dimensions, which are offset from the pivot axis so that the plate closely abuts the inboard edge of the platform floor when in a horizontal position.
In a typical Braun-type parallelogram-type lift, such as described in aforesaid application Ser. No. 08/843,497, the longer, lower push arm is pivoted to the platform at a location somewhat inboard of the platform pivot which supports the platform from the lifting arm extension of the parallelogram outer link. The distance between these pivots provides a lever arm, such that as the push arm is pressed down, the platform is caused to be rotated upwards to a stowed position. The push arm is braced by the shorter upper brace arm, both of which are coaxially pivoted to the slide block. As the lift is move above the transfer level, the slide block contacts the underside of the lower parallelogram link, and presses down on the push arm, causing upward rotation to the platform. Preferably, a spring assist, such as a gas spring, shown mounted diagonally across the lever arm assembly in the preferred embodiment of this invention, is used to bias the lever arm assembly so that the slide block is maintained at its most upward position in contact with the lower link to prevent free-fall on deployment of the lift platform downwardly from the stowed position.
The rotation of the inboard barrier plate to/from a horizontal bridging position to the vertical barrier position is accomplished by an actuator link spanning between one or both of the barrier plate side brackets and the push (lower) arm of the articulated lever arm assembly. The push arm of the invention, unlike the prior art push arms which are rigid struts, is a telescoping, variable length arm comprising an upper member telescoping over a lower member. The actuator link pivots from the lower portion of the upper member (outer sleeve) of the push arm. Since the actuator link is pivoted to the barrier plate inboard of the push arm pivot, a lever arm exists tending to rotate the barrier plate upon motion of the actuator link.
With the lift at ground level or in transit to the transfer level, the push arm is maintained at its maximum length by the gas spring, since the slide block is not yet in contact with the parallelogram link. The actuator link length is selected so that the barrier plate is rotated to a substantially vertical xe2x80x9cbarrierxe2x80x9d position in this configuration. As the lift approaches the transfer level, the slide block contacts the parallelogram lower link and pushes down on the push arm upper member (outer sleeve), causing it to telescope over the lower member. This in turn pushes down on the actuator link, causing the barrier plate to rotate towards a horizontal xe2x80x9cbridgexe2x80x9d position. The geometry of the actuator link and its pivot mounting brackets, and the telescoping range of the push arm are selected so that the barrier plate rotates to mate smoothly with the outboard margin of the vehicle floor sill as the lift arrives at the transfer position, with the barrier plate substantially horizontal. The barrier plate may have an inboard lip plate fixed to it and shaped to accommodate a smooth transition from bridge to vehicle floor.
As the lift moves past the transfer level towards the stowed position, the push arm becomes maximally telescoped, and thereafter acts as a rigid strut during stowage. Preferably there is an affirmative locking mechanism to control the precise length of the push arm during motion to storage. The principal embodiment has a stud located on the underside of the slide block adjacent its lower edge. As the lift approaches the stowed position and the lever arm assembly nests between the platform and parallelogram structure, the stud inserts first through a slot provided in the upper member of the push arm, and then continues to insert in a slot located in the upper part of the push arm lower member. The location of these respective slots is selected so that the stud move unencumbered through both slots to fix or pin the push arm upper and lower members to a predetermined telescoped length.
A preferred feature of invention is a safety load interlock system such as disclosed in our prior patent Goodrich, U.S. Pat. No. 5,261,779 issued Nov. 16, 1993 entitled DUAL HYDRAULIC, PARALLELOGRAM ARM WHEELCHAIR LIFT, at col. 12, line 65 to col. 13, line 38, which is incorporated herein by this reference. The interlock system may be mounted on, or adjacent to, the articulated lever arm assembly to detect the presence of a platform load greater than a selected cut-off weight. The interlock system also comprises aspects of the control system for the hydraulic lift cylinders and prevents the platform from raising above the transfer level, e.g., to stowage when a platform load is detected.
The barrier system of the invention may be used on both dual and single parallelogram type lifts. For use with a single parallelogram lift, appropriate modifications readily apparent to one skilled in the art can be made to the barrier and its support structure, the principles of its actuation remaining the same as with the dual parallelogram embodiments described below in detail.